Testing conservation delivery for curlew

Blog by Dr David Douglas, Principal Conservation Scientist; Dr Irena Tomankova, Conservation Scientist, and Sarah Sanders

The plight of the Eurasian curlew is now established as a major conservation priority in the UK. Based on the combination of global conservation status (IUCN Near-Threatened), the global importance of the UK breeding population (19-27%) and the rapid decline of the UK breeding population (-48% since 1995), RSPB and others have argued that the curlew should be considered the UK’s highest conservation priority bird species (Brown et al 2015).

A recently published study in Bird Study, led by BTO and co-authored by David Douglas of the RSPB (Franks et al 2017), adds to our knowledge of the factors associated with curlew declines. Using BBS data, the aim of the study was to examine whether there was national-scale support for drivers of population change identified from previous regional or site-based studies, such as predation or afforestation of open ground, and a range of other potential effects including climate. The study looked at correlates of abundance in two time periods separately, 1995-99 and 2007-11, and correlates of change in abundance between these two periods.

Full details of the results are available in the paper, but key findings are that arable farmland and woodland were both associated with lower curlew abundance and greater population declines. The woodland effect may relate to replacement of curlew breeding areas with woodland and also the role of woodland plantations in supporting higher generalist predator abundances including foxes. Curlew abundance was positively associated with extent of protected area coverage (such as SSSI’s, SAC’s and SPA’s). Climatic effects were also detected, with warmer temperatures and lower summer rainfall associated with lower abundance and more negative population change. Associations were found with aspects of game management; abundance was positively associated with higher abundance of some gamebirds; abundance and population change were negatively associated with numbers of generalist predators; abundance in the most recent period was negatively associated with the extent of moorland burning for red grouse.

Photo: Curlew, by Andy Hay (rspb-images.com)

How can we use this and other evidence to recover curlew across the UK?
Climatic impacts may become an increasing issue but are hard to manage, particularly in the short term. The current provision of protected areas for breeding curlew has been deemed insufficient (Stroud et al 2016) and is therefore not currently expected to play an important role in recovering populations. The study suggests that ensuring suitable breeding habitat and reducing predation pressure will be key interventions for conserving curlew. This supports RSPB’s view that testing the effectiveness of these managements is essential for informing curlew recovery.

Recovering the curlew is hugely important to RSPB and we have led efforts in the UK to co-ordinate action for the curlew. We have initiated a Curlew Recovery Programme to step up our efforts for this species, with the main scientific research currently being a Trial Management Project (TMP). Improving the prospects of a species that, whilst declining, still breeds widely across the UK uplands and in some lowland areas, will require large-scale delivery of conservation measures. Before advocating for such delivery, we need a reasonable level of certainty that any measures deployed can be effective. This is where trial management projects, testing the delivery of conservation interventions on a suite of sites, can play a role, and RSPB is a leader in delivering such projects. The curlew TMP is testing whether the combined delivery of habitat management and predator control is effective in improving curlew nesting success and breeding abundance. It is being conducted in six study areas across the UK, each with a trial site where the targeted management is delivered, and a reference site managed on a ‘business as usual’ basis. Sites include a mix of reserves and private farmland and include both enclosed in-bye grassland and unenclosed moorland, representing the main habitat types used by curlew breeding in the UK. The total study area is 114km2, making this one of the largest and most ambitious field studies ever undertaken by the RSPB.

The rationale for reducing predation pressure is that previous work (including Grant et al 1999) has identified low productivity as a major cause of the curlew decline - put simply, insufficient young are being raised to fledging. Predation of eggs and young has been identified as a major cause of this low productivity. The evidence therefore suggests that recovering curlew will require a reduction in predation pressure at breeding areas. However, will reducing predation alone be sufficient? To breed successfully, curlew need sufficient areas of suitable habitat in which to establish territories, conceal their nests and in which chicks can obtain sufficient invertebrate food to successfully fledge. Through research we can identify the mosaic of habitats that curlew associate with during the breeding season, but we need to test whether creating the right habitat delivers positive responses. We therefore think that the combination of delivering suitable habitat and reducing predation pressure will provide the best conditions for curlew to breed successfully and recover their populations, but need to test the effectiveness of this.

Photo: Curlew, by Tom Marshall (rspb-images.com)

Managing for curlews
Given that curlew are widely dispersed across vast areas of the countryside, what is the best way to manage habitats and reduce predation pressure at the landscape scale? Habitat management in the TMP is being undertaken by famers, contractors and reserve staff, guided by knowledge of what curlew require and attempting to create this on trial sites, using standard methods such as rush control, mowing and grazing.

There are various potential means for reducing predation pressure. Non-lethal methods include the removal of forestry plantations that can support predators, in the vicinity of curlew breeding areas, or the use of anti-predator fencing. Whilst removing such plantations would surely make an important contribution to reducing predation, it would probably be insufficient on its own and would take time to achieve over large areas, during which time curlew will continue to decline. Furthermore, national and devolved policies for woodland expansion are creating pressure to increase woodland, sometimes in important wader breeding areas, rather than remove it. Installing anti-predator fencing over the large breeding areas that curlew use across the uplands is simply not feasible.

Lethal control of predators is therefore a pragmatic solution to reducing predation pressure. This is not a solution that RSPB accepts lightly (see this recent blog from our Conservation Director), but for conserving a rapidly-declining species such as the curlew, which is known to be adversely affected by predation, the case is a strong one. Which predators should be targeted and how much effort should be put into reducing their impact on curlew, without seeking to eradicate them or impact adversely on their own population status? Collating evidence from a range of sources on i) effects on breeding curlew, and ii) which species can be most effectively controlled through legal culling, highlights foxes and also hooded and carrion crows as priorities for control.

Previous work has shown that predator control delivered at an intensity associated with grouse moor management can deliver positive results for curlew (Fletcher et al 2010). However, deploying full-time, year-round predator control across the UK range of the curlew, including areas outwith those subject to grouse moor management, is simply not affordable, and may not always be necessary. We are therefore testing whether a more affordable level of predator control, delivered specifically as a conservation tool for breeding waders, is effective for curlew. Predator control is delivered by experienced, professional contractors working at key times of year to reduce predation pressure on curlew. They use humane methods that comply with, and for some aspects exceed, legal requirements for controlling predators.

The project began with a baseline year of monitoring curlew, predators and habitat on all sites. We have subsequently been delivering the targeted habitat and predator management on the trial sites. As the study is only part-way through, it is too early to present detailed results. But as an indication of the management delivered to date, 159 foxes and 928 carrion and hooded crows have been killed across the trial sites. Habitat management has been undertaken on 385 hectares, including rush cutting, grazing and mowing to reduce sward density. The most recent field season of monitoring responses on trial and reference sites has just been completed and interim analyses will begin in earnest, with further seasons of management planned.

A key method for delivering land management with conservation as an aim is through agri-environment schemes. Advocating for new options, or wider deployment of current options, requires evidence of whether these are effective in achieving their objectives and are affordable. This forms the rationale for the management that we are testing and we hope that the results will inform the future roll-out of curlew conservation measures.

We thank Natural England for supporting the curlew Trial Management Project through the Action for Birds in England (AfBiE) partnership.

About the authors

Dr David Douglas works at the RSPB Centre for Conservation Science and leads RSPB’s UK upland research programme. This includes work to inform the recovery of declining species and also addresses wider land use issues including forestry, grazing, moorland burning and onshore wind farms, examining the impacts of these on upland species, habitats and the wider environment.

Dr Irena Tomankova works as a Conservation scientist at the RSPB Centre for Conservation Science, leading the delivery of science within the Curlew Trial Management Project.

Sarah Sanders manages the curlew recovery programme at the RSPB, which involves co-ordinating and supporting colleagues from across the organisation to improve the conservation prospects for this species.